math
posted by Hobo .
Lydia Rise us building a terraium and needs to buy two sizes of gravel and soil to go in the bottom. The terraiun is 24 in longs, 14 in wide, and 15 in tall.
A.The bottom layer is pea gravel and needs to be 2 inches deep. How many cubic inches will she need? B. The second layer is aquarium gravel and needs to be 1 inch deep. She has 400 cubic inches of gravel, does she have enough?C.The top layer is potting soil. It needs to be 5 in deep. The ptting soil comes in bags of 1,500 cubic inches. How many bags will she need?

How have you started these problems?
Where did you get stuck? 
this whole thing makes no sense to me. can you please answer it?

The major part of this problem involves volume.
The volume of a rectangular prism is:
V = l * w * h
Since the bottom layer is 2 inches deep 
V = 24 * 14 * 2
V = 672 cubic inches
Now figure out the volume of each of the other two layers.